Various types of safety latches, locks, door restraint mechanisms and fastening devices have been devised for preventing the opening of the door and the unauthorized intrusion of persons. Many such devices, such as deadbolt locks, can be picked, wrenched, or pried from the outside by intruders, and thus do not offer the individual the desired security. Other restraining devices, such as chain locking devices, have a low yield strength (partially because the door can be opened several inches), or allow the restraining device to be cut or otherwise deactivated by the intruder. Other devices which do not suffer from the above disadvantages are typically complicated and thus expensive, require a special tool to install the device, and/or are very unsightly when both activated or deactivated, so that such devices have not been widely accepted on either a commercial or residential basis.
U.S. Pat. No. 3,513,566 to Sipes and U.S. Pat. No. 3,809,418 to Canfield disclose chain-type door fastening devices. Sipes discloses a chain for engaging the doorknob and a pair of arms for engagement with a strike plate. Canfield discloses a similar chain used in conjunction with a strike plate having a portion faced interiorly of the door. Such devices depend on the effectiveness of the chain, and are both unsightly and do not generally offer the individual the desired high degree of protection against intruders.
U.S. Pat. No. 4,155,578 to Roland discloses a safety latch utilizing a strap and a wedge member designed to prevent opening of the door when the device is in place. U.S. Pat. No. 4,254,976 discloses a door restraining mechanism utilizing a spring to exert force between a door handle shoe and a pressure face positioned against the doorjamb. These devices, at least to some extent, utilize the frictional force of engaging members. Such devices likewise have not been widely accepted, possibly because they also do not actually afford the desired high degree of security, or possibly because they are not perceived as being likely to prevent the opening of the door by a determined intruder.
Various effective hinge-type latches have been designed, which employ a pin for joining both sides of the latch. Such a simplistic latch is shown in conjunction with a window in U.S. Pat. No. 1,659,822 to Innes. Such a hinge-type latch could also be used in conjunction with a swinging door, as shown for example in FIG. 1 of U.S. Pat. No. 4,015,868 to Buttler. Finally, U.S. Pat. No. 2,396,982 to Bousquet discloses a latching device for a swinging door which comprises a plurality of plates for positioning between the door and the doorknob, a pin, a plate adjacent the pin, and another plate having a portion designed for insertion in the bolt keeper of the door frame when the lock is applied to the door. The latter device is both complicated in operation and very unsightly, while the former devices clearly marr the door when installed and also detract from the aesthetic appearance of the door.